1. Field of Invention
The invention relates to an ink droplet ejecting apparatus and method that produce a printed record by ejecting an ink droplet.
2. Description of Related Art
An ink jet print head used in a piezoelectric ink jet printer includes a cavity having a pressure chamber and a piezoelectric actuator provided adjacent to the pressure chamber in the cavity plate. A predetermined driving pulse is applied to the piezoelectric actuator, so that the volume of the pressure chamber is changed. With generation of a pressure wave in the pressure chamber according to the volume change of the pressure chamber, an ink droplet is ejected from an orifice. Further, a dot having a desirable density can be formed with a plurality of ink droplets by a plurality of driving pulses successively applied to the piezoelectric actuator at a time.
For example, when a dot having a high density is formed, two successive driving pulses are applied to the piezoelectric actuator to form a dot with two ink droplets.
However, at the time of ink ejection, there is a case where an ink droplet, which is an undesired ink droplet called a satellite ink droplet, may be produced other than a main ink droplet that is to form a dot, when the plurality of driving pulses are applied to the piezoelectric actuator as described above. This is caused by a residual pressure in the cavity. In a case where ink droplets are successively ejected by application of a plurality of driving pulses, a pressure wave remaining in the cavity does not completely flatten out after ejection of the main ink droplet, so that the undesired ink droplet is ejected by the residual pressure. The satellite ink droplet degrades the quality of printing, such as characters and images.
Therefore, in a conventional ink jet printer, a cancel pulse is included in a driving waveform to avoid occurrence of the satellite ink droplets. For example, when two driving pulses are applied to the piezoelectric actuator, a cancel pulse is applied after application of a second ejection pulse. Alternatively, a first cancel pulse is applied after application of a first ejection pulse and then a second ejection pulse is applied. After that, a second cancel pulse is applied. The cancel pulse reduces the residual pressure wave oscillation in the cavity after application of a preceding driving waveform. Though the application of the cancel pulse to the cavity develops a pressure in the cavity, the pressure is not strong enough to cause ejection of an ink droplet.
However, even when the cancel pulse is applied to the piezoelectric actuator as described above, the satellite ink droplets are produced or formed dots are deformed due to variations in quality of the ink jet print heads.
With the increase in the number of application of pulses, the pressure wave oscillation in the pressure chamber becomes complicated. Thus, there may be a case where the residual pressure is difficult to reduce.
The invention provides an ink droplet ejecting apparatus and method that prevents the occurrence of satellite ink droplets to improve printing quality.
According to an exemplary aspect of the invention, ejection of an ink droplet is implemented by a driving pulse being applied to an actuator provided in an ink droplet ejecting apparatus that includes a cavity plate having a pressure chamber for ejecting an ink droplet and the actuator that generates a pressure wave in the pressure chamber.
In the ink droplet ejecting method, an output period of a sequence of driving pulses is set to be five times of AL, where AL is the time in which a pressure wave propagates one-way within the ink chamber, when the sequence of the driving pulses are successively output to form one dot with a plurality of ink droplets in accordance with a printing command.
According to the ink droplet ejecting method of the invention, when the sequence of the driving pulses are successively output to form one dot with a plurality of ink droplets, the output period of the driving pulses is set to be five times of AL, where AL is the time in which a pressure wave propagates one-way within the ink chamber. Therefore, the residual pressure is reduced so that a second ink droplet is stably ejected in the appropriately reduced residual pressure. Consequently, ink droplets can be stably and successively ejected without consideration given to the amount of the residual pressure in the pressure chamber and the cancel of the residual pressure.
According to another exemplary aspect of the invention, an ink droplet ejecting apparatus includes a pressure chamber that contains ink, a nozzle that communicates with the pressure chamber and can eject the ink contained in the pressure chamber, an actuator that changes a volume of the pressure chamber, a driving pulse generator that generates a driving pulse to be applied to the actuator and a controller that allows the nozzle to eject an ink droplet therefrom by selectively applying the driving pulse generated by the driving pulse generator to the actuator to generate a pressure wave in the pressure chamber. In the ink droplet ejecting apparatus, the controller sets an output period of a sequence of driving pulses to be five times of AL, where AL is the time in which a pressure wave propagates one-way within the ink chamber, when the sequence of the driving pulses are successively output to form one dot with a plurality of ink droplets in accordance with a printing command.
According to the ink droplet ejecting apparatus, when the sequence of the driving pulses are successively output to form one dot with a plurality of ink droplets, the output period of the driving pulses is set to be five times of AL, where AL is the time in which a pressure wave propagates one-way within the ink chamber. Therefore, the residual pressure is reduced so that a second ink droplet is stably ejected in the appropriately reduced residual pressure. Consequently, ink droplets can be stably and successively ejected without consideration given to the amount of the residual pressure in the pressure chamber and the cancel of the residual pressure.